My bosses flight back to the US (CDG-LHR-RDU)

has been impacted by the cancellation today of BA308 (the CDG - LHR leg)

Couple of question for anyone who can help

1) can someone find out the nature of the cancellation
2) regarding EU261 compensation (subject to the above reason of course). How does that work as the LHR - RDU leg is operated by AA.

I believe the trip is ticketed by BA